In the field of mobile electronic devices such as mobile telephones, because of its superior waterproofness, dustproofness, and rustproofness, so-called contactless charging, which is charging without going through an electronic contact such as between a mobile electronic device and a power cable, has come into widespread use. There are a number of systems for contactless charging. One is electromagnetic induction type contactless charging using electromagnetic induction between a power transmitting coil of a charger and a power receiving coil of a device to be charged. The Qi standard of the WPC (Wireless Power Consortium) has been established as an international standard for contactless charging. This enables a single contactless charger to handle charging of different mobile devices.
A contactless power transmitting device aimed at achieving a thinner power transmitting coil and power receiving coil used in contactless charging has been proposed (refer to, for example, Patent Document 1 noted below). Patent Document 1 discloses a contactless power transmitting device having a power transmitting device functioning as a charger, a power receiving device (first mobile telephone) that includes a secondary battery functioning as the power supply for the main unit of a portable telephone, and a power transmitting-receiving sharing device (second mobile telephone) functioning as a charger and including a secondary battery that serves as a power supply for the main unit of a mobile telephone.